Pyrolysis of myrtenyl compounds to monocyclics and acyclics



232L547 PULYSHS 9F TENYL COMPQUS E MONUCYCLMJS At ACYCLICS Eugene A.ein, llachsone, Fla, or to The ggidden Company, Clcved, Ohio, acorporation of No Drawing. Applieafion June 12, 1953 Serial No. 361MBllll @laims. (Cl. 26Md9) This invention is concerned with the thermalisomerization of myrtenyl compounds to perillyl compounds and certainother valuable products.

it is known that myrtenol is present in certain natural essential oilsand also that myrtenol and myrtenaldehyde may be produced syntheticallyas by selenium dioxide oxidation of a-pinene or air oxidation offl-pincne followed by certain suitable recovery steps. It is also knownto convert myrtenol to myrtenal. Numbers of esters of myrtenol are knownas well as myrtenyl chloride and bromide, myrtenyl ethyl ether, myrtenicacid, etc. We have found that myrtenol, its derivatives and analoguesare capable of yielding corresponding perillyl compounds when treatedthermally, and, in addition, certain novel and valuable isomers areproduced. Perillylaldehyde and perillyl alcohol are constituents ofcertain natural oils.

It is known to convert the alcohol to the aldehyde and the reverse.

Perillyl compounds are valuable not only as odorant and flavoringmaterials but are suitable intermediates for producing perillaldoxime,one form of which is known to be a very powerful sweetening agent suitedfor uses such as sweetening tobacco and foods. therefore, to provide aprocess for converting myrteuyl compounds to members of the perillylseries.

Accordingly, among the objects of this invention are:

To provide a process for converting members of the myrtenyl group tomembers of the perillyl group.

To provide a process for converting myrtenol to perillyl alcohol andother valuable compounds.

To provide a process for converting myrtenal to perillaldehyde and othervaluable compounds.

To provide a process for converting myrtenyl compounds to a sweeteningagent.

To provide a process for converting the cheap and available pinenes tovaluable members of the perillyl group of compounds.

To provide a process for converting myrtenyl compounds to novel acycliccompounds of the allo-ocirnene type.

To provide a process for converting myrtenyl compounds to novelcompounds of the pyronene type.

To provide a process for converting pinene oxygenated at the 7-positionto 1,8-p-menthadiene oxygenated at the 7-position.

Other valuable objects will be apparent to those skilled in the art.

I have found that myrtenyl compounds when heated in the vapor phase orin the liquid phase yield the corresponding perillyl compoundsaccompanied by isomeric allo-ocimene and pyronene type compounds andthat polymeric material is also produced in the pyrolysis and/orpurification procedures and that this polymeric material containsallo-ocirnene type polymer. The proportions of the various classes ofcompounds that can be isolated depends on the pyrolysis conditions andthe procedures employed in working up the products of pyrolysis.

The starting myrtenyl compound may be produced by any convenient methodand may be of either optical sign or racemic. in general, thermalracemization' occurs to such an extent in the process that the productsof pyrolysis possess but feeble optical activity irrespective of thehigh It is desirable,

2,Zi,h'dl Watented den. 8, was

2 degree of optical activity possessed by the initial myrtenyl compound.

The myrtenyl compound is suitably treated at about 225 C. to 700 C. fora time sumciently long to bring about its substantial conversion to thecorresponding acyclic and monocyclic compounds. The time required isrelated inversely to the temperature employed. Thus the myrtenylcompound may require heating for several hours in the lower temperatureranges or for only a small fraction of a second at the highertemperature ranges. The upper temperature limit is one imposed byequipment problems rather than a limitation of the pyrolysis. Ingeneral, it will be found convenient to operate in the liquid phase andfor longer periods of time where the temperature to be maintained is ofthe order of 225 to 300C and in the vapor phase where a temperature of400 C. or above is employed, though liquid phase pyrolysis at hightemperatures and short contact times, as by continuous feed throughapyrolysis tube under pressure maintained by a pump, is satisfactoryalso. Where the boiling point of the myrtenyl compound is of the orderof 225 C. or above, then heating at or below the reflux temperature isgenerally satisfactory, but for the lower boiling myrtenyl compounds,such as myrtenyl methyl ether, faster conversions will beattained byautoclaving. Of course, if the myrtenyl compound employed is a highboiling material so that it cannot be readily vaporized by heat or byheat assisted by sparging with an inert gas, then it is most suitablytreated in the liquid phase.

I have found that the pyrolysis product may be conveniently separatedinto fractions enriched in the various pyrolysis products by means offractional distillation most suitably in vacuo where the boiling pointis high or where the product is not completely stable at its boilingpoint at atmospheric pressure. Alternatively, the reactive pyrolysismixture can be subjected to other separation processes, or, if desired,it can be converted to derivatives which can then be separated by takingproper advantage of the ditierences in physical and/or chemicalproperties that exist in the types of compounds in hand.

llt has been found that suitable myrtenyl compounds for conversion toperillyl compounds and the other classes of thermal conversion productsinclude myrtenol, myrtenal, acetals and cycloketals, myrtenyl ethers andesters and, in general, those compounds bearing substituents on the7-carbon atom of the pinene structure. It is preterred, however, forbest results not to use those compounds whose substituents are of such anature that under the influence of heat they cause undesirabledehydration, polymerization or otherwise adversely affect the course ofthe pyrolysis, such, for example, as myrtenyl sulfate or acid sulfate,etc. In other cases, such as to: the formation of perillyl halides,better results are ob tained by pyrolysis of myrtenol followed byconversior of the monocyclic alcohol to the halide. Further, where theprimary pyrolysis products are desired, the pyrolysi: of such esters asmaleic esters is not desirable, since the initial pyrolysis productswould tend to resinify due tr the presence of mixed dienophiles. In thecase of the aldehyde, similar condensable systems are inherently present in the pyrolysis mixture and when pyrolyzing myr tenal, it isdesirable to avoid unnecessary conditions ac celerating the condensationreaction, unless resinou: products are the ones desired.

In general, therefore, since the myrtenyl compound most readily andinitially available from synthesis mix tures are the aldehyde, alcoholand esters, when este: type separation has been employed to separate thesyn thesis mixture, and since these products are well Sllllfll topyrolysis, we prefer to employ these compounds to 3 pyrolysis and toconvert their pyrolysis products to other derivatives after pyrolysis ifand as desired.

The flow sheet indicates the nature of the pyrolysis which myrtenylcompounds undergo. As a specific example, the conversion of myrtenal toperilladehyde and other volatile compounds is shown. The non-volatilematerial produced is presumed to be largely an alloocimene aldehydepolymer or condensation product. The cyclohexadiene aldehydes arepresumed to be derived by cyclization of allo-ocimene aldehyde. Thealloocimene aldehyde and its cyclization and polymerization products areuseful as dienophiles for manufacture of resinous products, whereas theallo-ocimene aldehyde and its cyclization products also condense withacetaldehyde, acetone, etc. to form products of pleasant characteristicodors. Perillaldehyde also condenses with acetone, etc., as is known,and also converts readily to the intensely sweet oxime.

The pyrolysis product produced by heating the myrtenyl compound isreadily separable by fractional distillation where the products aresufliciently volatile and enriched or pure fractions of the acyclic, theconjugated cyclohexadiene and the perillyl compound can be separated andthe individual components can be subjected to other conversions such aseither selective or saturative hydro genation, oxidation, etc.Alternatively, it will be found convenient in certain cases to react thewhole pyrolysis product and then separate the desired pure derivatives.Thus, perillyl acetate can be prepared by separating the perillylalcohol from the pyrolysis product of myrtenol, then esterifying it, orit can be prepared by esterifying the whole pyrolysis product, thenseparating the desired ester. If rather sensitive compounds areinvolved, as in the case of the aldehyde constituents of myrtenalpyrolysis, it is found preferable in some cases to condense withacetone, hydroxylaminc, etc. and then fractionate the more stablederivatives when it is desired to produce those derivatives.

The following examples are illustrative of our inven- EXAMPLE 1 Puremyrtenol (500 g., 11 1.4950, 49 [10 cm. tube] was pyrolyzed in the vaporphase by introducing the liquid dropwise at 2 cc./rnin. down the side ofa vertical standard iron pipe maintained at 400 C. The tmeperature wasdetermined from a thermocouple inserted down the center of the pipe.

An infrared spectrogram on the total pyrolysate showed:

(1) That it contained very little unchanged myrtenol;

(2) An absorption band at 13.7 characteristic of aand fi-pyronene;

(3) CH =C absorptions at 11.25 4 and 6.0;;

(4) A carbon to carbon conjugation absorption at 6.23%

(5) A broad primary alcohol absorption between 9.4 1

and 1045 and (6) A carbonyl absorption at 5.95;.

The ultraviolet spectrogram of the pyrolysate showed at 278 m andinflection points at about 270 m and 286 mp to form a curve of the shapeexhibited by alloocimene type compounds and related conjugated trienes.

The product was fractionally distilled using an efficient column packedwith glass helices. The column was operated at 10 mm., absolutepressure, to a head temperature of 97 C. and then the absolute pressurewas dropped stepwise to a final value of 0.5 mm., and the distillationcontinued to a pot temperature of 260 C. Twenty-two fractions werecollected throughout the distillation and ranged in size from 3.0 to29.5 grams. Infrared and ultraviolet spectrograms were made for most ofthe fractions and these indicated the number of major pyrolysis productsas well as the composition and quantity of the major products. Thefollowing compounds in order of their increasing boiling points werefound to be present;

(A) Carbonyl and alcohol compounds of unknown structure comprised thefractions boiling from 53-85 C. at 10 mm. The presence of the functionalgroups specified was shown by infrared spectrophotometric analysis.

(B) a-Pyronenc and fi-pyronene alcohols. a-isomer,5,5,6-trimethy1-1,3-cyclohexadiene-1-carbinc1, and fl-isomer,1,6,6-trimethy1-1,3-cyclohcxadiene-Z-carbinol, were the major componentsof the fractions boiling from -97 C. at 10 mm., and 53-60" C. at0.5-0.15 mm. The refractive index of the fraction richest in thesealcohols was 1.4987 at 25 C. They were identified and characterized asfollows:

(1) Theultraviolet spectrograms of the fractions containing theseproducts had a at 264 mi in iso-octane and a specific extinctioncoefiicient (a=Ei'.'h) of 22-27 The )5, reported in the literature forthe mand ppyronenes is 264 my, and an a of 2 9-415. The higher value ofthe extinction coefficient is to be expected for the hydrocarbonsbecause of the higher concentration of the particular conjugate systemexhibiting ultraviolet absorption in the hydrocarbons as compared to thehigher molecular weight of the alcohols and the corresponding lowerconcentration of the absorbing system in the latter.

(2) The infrared spectrograms of the fractions containing the productshad a broad major absorption at l3.713.9n which covers the range of themajor absorptions in ozand [it-pyronene. Also present in the spectra ofthe products was a broad alcohol absorption between 9.3 and 10.2 1 whichis in the region for a non-associated primary alcohol absorption. Thealcohols consequently contained the pyronene nucleus and were primaryalcohols and therefore are the products specified. This mixture ofalcohols is characterized further by possessing infrared absorptionbands at 8.27, 8.55, 8.82. 9.53. 9.95, 10.95, 11.25, 11.50, 12.45 and13.73;. These bands vary somewhat in relative intensity from fraction tofraction thus indicating the presence of two pyronene alcohols even inthe purest fraction obtained. The remainder of the spectrum of theproducts was also very similar to that of the pyronenes.

(C) Perillyl alcohol, 11 1.5021, e 0.84 in a 10 cm. tube. was theprimary product found in the fraction boiling between about 60-65 C. atabout 0.15 mm. The low rotation of the best fraction was attributed toracemization during pyrolysis. It was identified and characterized asfollows:

(1) The major infrared absorptions of the fractions were at thesewavelengths: 13.20, 12.87, 12.18. 11.24, 10.89, 10.02, 9.80, 9.47, 9.00,8.7], 8.58, 8.08, 7.22, 6.00, 3.00 From the wavelength, shape andoptical densities of the absorptions, the compound was found to containthese groups:

(a) Broad primary alcohol absorption between 9.3 and 10.21:.

(b) CH =C absorptions at 6.05, 10.85 and 11.2 the last two forming adoublet of the shape and intensity as in the spectrum of limonene. The11.2 absorption is of much higher optical density than the one at 10.85like limonene.

(c) A tri-substituted ethylene absorption at 12-1l2-4[I.. This is aslight displacement from a similar absorption in limonene. Thedisplacement is probably due to the fact that the double bond is part ofan allylic system which is not present in limonene.

(2) The compound when refluxed with concentrated hydrochloric acidformed cymene, thus showing it to be a pmenthane derivative.

This evidence conclusively shows the product to be perillyl alcohol.

(D) An alloocimene alcohol, 2-methyl-2,4,6-octatriene-6-carbino1, wasthe chief material present in the fractions boiling 72-95 C. at 0.5 mm.It was identified and characterized by spectrophotometric methods asfollows:

(1) its ultraviolet spectrum in iso-octane had a a at about 278 m and aspecific extinction coefficient The shape and position of the absorptionmaximum and inflection points for this spectrum was the same as for thespectrum of the hydrocarbon alloocimene. That is, besides the A at 27811111., there were inflection points at about 270 and 286 m just asalloocimene shows. The specific extinction coefficient of the alcoholwas of the same comparative magnitude as that of alloocimene.

(2) The infrared spectrum showed major absorptions at the followingwavelengths: 6.95, 7.28, 7.90, 8.14, 8.52.

9.50, 10.13, 10.55, 11.50, 11.93, 12.30 and 12.80 1. The

wavelengths underlined are those of absorption bands common to both thealcohol produced here and alloocimene. The absorptions at 9.50 and10.13;: form a broad band which shows the presence of a primary alcohol.

The viscous semi-resinous distillation residue was alloocimene alcoholpolymer since it possessed an ultraviolet spectrum showing t at 242 mjust like that of alloocimene polymer. Furthermore, when distilledfractions rich in alloocimene alcohol were heated at 210 C. for tenhours, the product was shown to contain a much lower extinctioncoetficient than before heating and the absorption maximum at 242 mcharacteristic of alloocimene type polymers had become quite strong.

Analytical data comprising fractionation data and data from the spectraof the fractions showed that there was present in the crudeisomerization product:

p Percent Unknowns 5.7 Pyronene alcohols 25.0 Pen'ilyl alcohol 36.0Alloocimene alcohol. 15.3 Distillation residue 115.0 Overall loss .1 -13.0

Total -s 100.0 Largely allooelmene alcohol polymer.

EXAMPLE 2 Pure myrtenol was sealed in evacuated glass capsules. Thecapsules were then heated at 257-265 C in an oil bath. Infrared spectraon samples taken from capsules heated fonperiods of from one to livehours showed the isomerization to be essentially complete after threehours .heating at this temperature. Very little pyronene or a1loocimencalcohols were present as compared with material pyrolyzed in the vaporphase as in Example 1. yield of perillyl alcohol was about 47% asdetermined by spectrophotometric analysis by comparison of infraredspectra of the pyrolyzed myrtenol'wtih the spectrum of pure perillylalcohol produced by efiicient fractionation of crude pyrolysis productsas in Example 1.

This product contained a substantial amount of polymer resulting frompolymerization of the alloocirnene alcohol L in the liquid phase. Thispolymer is characterized by a strong ultraviolet absorption band withmaximum absorption at about 242 m i EXAMPLE 3 "About 50 grains ofpure'myrtenol was refluxed at 220-240? C. abatintpsphr'ic pressure for atotal of 13% hours. Infrared spectra were run on samples of the re-'*action mixture taken after 2, and 13% hours of reanalysis employing asanoptical standard pureperillyl alcohohpro duced by fractionation of crudemyrtenol pyro1ysis nixftujresf in Example 1. On removal of 1" volatileniateii al in'vlacuuni, primarily perillyl alcohol,

The

there remained a residue substantially non-volatile at 160 C. at 10 mm.This semi-resinous product, characterized by its showing infraredabsorption bands located in the region where primary alcohols showabsorptions 6 and possessing a strong ultraviolet absorption with a at242 m consisted of alloocimene alcohol polymer.

EXAMPLE 4 Pure myrtenyl acetate, n 1.4706, =-46 (10 cm.

10 tube), (1056 grams) was refluxed at 223-242 C. for 26 hours. Infraredspectra on the reaction mixture at various intervals showed the progressof the isomerization. During the pyrolysis, some acetic acid was formed.

After 11 hours of heating, the presence of the acetic acid 15 hadlowered the pot temperature below 230 where little isomerizationoccurred. From then on, the acetic acid was distilled off to maintain apot temperature above 230 C. Very little change in the composition tookplace in the last 7 hours of heating.

The reaction mixture was then fractionated through an etiicient columnpacked with glass helices. The distillation was conducted at 10 mm.,absolute pressure, to a pot temperature of 210 C., and then the pressurewas reduced to 2.5 mm., and the distillation continued to a final pottemperature of 220 C. Twenty-three fractions were collected and theseranged in size from 9 to 51 grams. Infrared and ultraviolet spectra weremade for most of the fractions, and these indicated the number of majorpyrolysis products as well as their composition and 3 quantity. Thefollowing compounds in order of their increasing boiling points werefound to be present:

(A) Hydrocarbons comprised the material boiling 39-4525 C. at 10 mm. Theabsence of oxygen-containing groups was shown from the infrared spectraof the fractions in this boiling range.

(B) a-Pyronene audit-pyronene acetates and unidentitied esters were themajor/lcomponents of the fractions boiling atl04-l20" C., at 10 mm.Infrared spectrophotometric analysis showed the presence of thefunctional 40 groups as well as the pyronene structures. Ultravioletspectrophotometric analysis confirmed the presence of the pyronenes by9. A at 264 ms. The concentration of the pyronene acetates was not over20% in the total fractions containing them.

(C) Perillyl acetate, r2 1.4780, was the major compound boiling at 124C, at 10 mm. It was characterized and identified from its infraredspectrum as follows:

(1) The major absorption bands were at the following wavelengths'(a):5.77, 6.12, 6.958, 7.348, 8.0513,

8.52, 8.7, 9.58, 9.77, 10142, 10.9, 11.2513, 11.8, and 12.3.

The absorptions marked B" are the center points of broad bands.

2) The primary acetate absorptions were those at 5.77, 8.05, 9.58, and9.77

(3) The CH =C absorptions were at 6.12 and 1 1.25;! a

(4) The trisubstituted ethylene group was represented v by theabsorption at" 12.3

Perillyl acetate has amild fruity odor.

(D) 'Alloocimene acetate, or 2-methyl-2,4,6-octatriene- 6-carbinolacetate, 11 1.5230, was the primary compound boiling at 102 C., at 2.5mm. It was character ized and identified 'fronfits infrared andultraviolet spectra as follows: i i

"(1) The major infrared absorption bands were at the followingwavelengths )i 5.76, 6.08, 6.92, 7.3, 8.0513, 9158, 9.82, 10.15, 10.45,11.42, 11.9, 12.34, 12.52. The absorption 'marked 13" is the centerpoint of a broad band.

(2) The ester group is represented by the bands at 5.76, 8.05', 9.58and9.82n.'

W (3) The; ultraviolet absorption maximum Ji was at "272 m with'aspecific extihction coeflicient 7 in iso-octane. The spectrum also hadinflection points at 267 and 285 m to form a curve of the same shape andin the same location as produced from allo-ocimene itself.

A large viscous, semi-resinous distillation residue was shown to containalloocimene acetate polymer from its ultraviolet spectrum which had a aat 240 01g and a specific extinction coefiicient of 29 and alsoinflectron points at 235 and 248 m This type curve 18 charav teristic ofthe basic alloocimene polymer structure.

Analytical data comprising fractionation and spectral data showed thatthere was present in the crude isomerization product:

. Percent Hydrocarbons 1.5 Unknown acetates and pyronene acetates 9.5Perillyl acetate 43.5 Alloocimene acetate 4.0 Distillation residue(largely alloocimene acetate polymer) 32.0

Loss, largely acetic acid and hydrocarbons 9.5

Total 100.0

EXAMPLE 5 Myrtenal (450 grams) was pyrolyzed in the vapor phase byadding the liquid dropwise at 2-3 cc. per minute down the side of avertical A" standard iron pipe maintained at 380-400 C. The temperaturewas determined from a thermocouple inserted down the center of the pipe.The product contained about grams of a sohd polymer that was removed byfiltration.

An infrared spectrogram on the liquid portion of the pyrolysate showed:

(1) That it contained very little unchanged myrtenal;

(2) A broad absorption band at 13.6 characteristic of basic aandfi-pyronene structures;

(3) A CH ==C aborption at 1l.2

(4) Carbon to carbon conjugation absorptions at 6.35 and 6.4;; and (5)Several absorptions between 5.75 and 6.15;; which represented differentconjugated carbonyls and a The product was fractionally distilledthrough an eificient column packed with glass helices. The distillationwas'conducted at 10 mm. to a pot temperature of 200 C., and then theabsolute pressure was maintained at 1-2 mm. to a final pot temperatureof 220 C. Twelve fractions were collected throughout the distillationand these ranged in size from 13 to 24 grams. Infrared and ultravioletspectrograms were made for all of the fractions and these indicated thenumber of major pyrolysis products as well as their composition andquantity. The following compounds in order of the increasing boilingpoints were found to be present:

(A) Highly conjugated carbonyl material of unidentilied structure wasthe major component of the fraction boiling from 50-76 C., at 10 mm. Theultraviolet spectrogram in iso-octane of this material showed a a at 237m with a specific extinction coefficient (a=E{f;,,,) of 38.2 and a a at271 m with an a. of 22. These data indicated the presence of a highlyconjugated system(s). The infrared spectrogram had major absorptionbands at the following wavelengths (a): 5.87, 5.97, 6.10, 6.30, 6.90,7.00, 7.30, 7.65, 8.26, 8.50, 8.70, 9.10, 9.35, 11.25, 12.07, 13.45,14.35, 14.54. The following structural features were indicated from thepresence of certain absorption bands:

5.87 and 5.97 Conjugated carbonyl.

6.10 and 11.25u CH;=.C

13.45; symmetrically disubstituted ethylene grouping.

(B) 5,5,6 trimethyl-1,3 cyclohexadiene 1- carboxy aldehyde was theprimary constituent of fractions boiling at 76-84" C., at 10 mm., m,1.4903-1.4979. These fractions had a sharp aldehyde-like odor.Ultraviolet and infrared spectrograms on these fractions indicated thepresence of one major compound. The ultraviolet spectrograms had a A at297 m and an a of 24.8 in iso-octane. The position of the a indicated alinearly conjugated system of the type C=C =CC= Safranic acid andpionone, which'have this structural system, yield ultravioletspectrograms with a 71,, between 280 and 300 mu, the exact positiondepending upon the solvent employed. The A of5,5,6-trimethyll,3-cyclohexadiene-l-carboxaldehyde was at 305 mp inmethanol with an a of 25. The shift in the A. with the change in solventindicated a conjugated carbonyl system. The infrared spectrograms ofthese fractions boiling at 76-840 0.. at 10 mm., had major absorptionsat the following wavelengths (p): 5.85, 5.95, 6.42, 6.86, 7.11, 7.30,7.37, 7.57, 7.95, 8.20, 8.56, 8.68, 8.85, 9.23, 9.53, 9.68, 9.87, 10.02,10.97, 11.23, 11.80, 12.40. 13.48. From the infrared absorptions, thefollowing structural features were indicated:

5.85 and 5.95 Conjugated carbonyl. 6.42;; Carbon to carbon conjugations.13.48;: symmetrically disubstituted ethylene group.

The symmetrically disubstituted ethylene absorption is explained fromthe fact that some highly conjugated carbon-to-carbon systems produce aninfrared absorption representing a resultant 2,3-double bond from a 1,4unsaturated system.

If the pyrolytic cleavage of myrtenal follows the rest of the myrtenylseries, then this linearly conjugated system 18 present in one of thesetypes of compounds: pyronene, p-menthane, acyclic. If it were part ofeither of the latter two basic structures, it should boil higher thanperillyl aldehyde or 7-methyl-2,4,6-octatriene-Z-carboxaldehyde, whichis not the case. Therefore, it is part of the pyronene system. Thus,from the data presented, the compound is5,5,6-trimethyl-1,3-cyclohexadiene-l-carboxaldehyde.

Further evidence for the structure of 5,5,6-trimethyl-1,3-cyclohexadiene-l-carboxaldehyde was derived from its acetonecondensation product. Five grams of this compound was added to a mixtureof 20 grams of acetone and 0.25 gram of solid sodium hydroxide at 25-30"C. The reactants were stirred for 2 hours after all the aldehyde hadbeen added. The mixture was then concentrated at about 150 mm. to a pottemperature of C. The residue was washed with sodium carbonate solutionto yield a product which had an odor reminiscent of hay and raspberries.The infrared spectrum of this product was similar to the spectra offi-ionone which provided more proof of the proposed structure of5,5,6-trimethyl- 1,3-cyclohexadiene-l-carboxaldehyde, because the basicstructures of fi-ionone and this compound would be very much alike. Theultraviolet spectrum of the product in iso-octane had a a at 226 m withan a of 21.3 and at a at 327 m with an a of 40.3. The shift in the afrom 297 m for the original carbonyl compound to 327 m for the acetonecondensation product indicated the longer linearly conjugated systemthat was formed by the condensation with acetone.

(C) 1.6.6 trimethyl-l ,3-cyclohexadiene-Z-carboxaldehyde and/ or (D)2,3,3 trimethyl-l,4-cyclohexadiene 1-carboxaldehyde was the majorcompound in the fractions boiling at 91-925 C., at 10 mm. (n1.4853-1.486l). It was identified from its ultraviolet and infraredspectra as follows:

(1) The ultraviolet spectrum of the fraction containing the compound inthe greatest concentration had a A at 237 m with an e of 33.8 in isooctanc. The A for the same material in methanol was at 243 m with an of34.3. The shift in the h indicated a conjugated carbonyl system. Theposition of the A would tend to support the structure in which thecarbon-tocarbon double bonds were not conjugated (D). However, verylittle is known about the ultraviolet spectra of compounds with thisconjugated system:

I l I (2) The infrared spectrogram of the same traction described in (1)had major absorption bands at the following wavelengths t): 5.85(broad), 6.37, 6.86, 7.05, 7.33, 7.95, 8.55, 8.80, 9.48, 9.66, 9.78,10.33, 10.53, 12.05, l2.40, 12.81, 12.90 and 13.55.

By summarizing the spectral data and applying the same line of reasoningas is presented in the last paragraph of section (B) of this example,the compound boiling at 91-925 0., at 10 mm., is either (C) or (D).

The acetone condensation product was prepared by the same procedure asthat described for compound (B). It had a hay-like odor. The infraredspectrogram was similar to that of p-ionone and the ultravioletspectrogram had a A at 278 m in iso-octane (ultraviolet spectrograms offi-ionone in hexane has 2. k at 280 mu).

(E) Perillylaldehyde was the major compound boiling from 101 (3., at 10mm, to 75" 0., at 1.3 mm, r1 15042-15059; literature, b 104-105 C, r115049-15060. The compound had a strong cuminlike odor as is reported inthe literature.

The intensely sweet perillylaldehyde oxime was prepared as definiteidentification of compound (E). The oxime was prepared by adding asolution of 25 grams of liydroxylarnine hydrochloride plus 50 grams ofsodium acetate in 75 cc. of water to a solution of 21.5 grams ofperillylaldehyde in 100 cc. of methanol. The temperature was maintainedat 25-30 C. The precipitate which formed was intensely sweet. The solidwas separated by filtration and then recrystallized from light naphthato give 21 grams (90% yield) of perillylaldehyde oxime, M. P. 101 C.(uncorrected), [a] =0. 'lhe ultraviolet spectrogram oi the oxime inmethanol had a h at 233 III/J. with an a of 124. The infraredspectrom'am of the crime had major absorption bands at the followingwavelengths (a): 3.0, 6.08, 7.67, 7.75, 8.45, 10.20, 10.48, 10.67,11.23, 12.20, 12.30, 12.47, 14.10.

The crystalline oxime itself did not have a sweet taste perhaps becauseof low or slow solubility, but when die solved in an organic hydroxylicsolvent, the solution was intensely sweet.

Further characterization of perillylaldehyde was made from itsultraviolet and infrared spectra as follows: Ultraviolet: a 226 m a,9l.5in isooctane A 230 m a, 91.6 in methanol The displacement of the h witha change in solvent indicated a conjugated carbonyl system. From therules developed by R. Woodward, I. A. C. S. 64, 76 (1942), the A forperillylaldehyde in methanol would be predicted at about 235 mp.Therefore, the actual value of the A 230 m l, added proof to thepresence of perillylaldehyde.

Major infrared absorption hands (a): 5.93, 6.02, 6.87, 6.95, 7.02, 7.15,7.26, 7.66, 3.05, 8.22, 8.55, 8.72, 9.58, 9.90, 10.00, 10.12, 10.30,10.58, 10.87, 11.23 (broad), 12.27, 12.95, 14.50. From the infraredabsorptions the following structural features were indicated:

5.92/L -a Conjugated carbonyl. 6.02 and 11.23;]. CH C group 12.27 and12.95 2 Trisubstituted. ethylene group.

(F) 2-methyl-2-,4,6-octatriene-6-carboxaldehyde, alloocimene aldehyde,was present in the fraction boiling at 90 C. at 1 mm. It was identifiedand characterized as follows:

(l) The ultraviolet spectrum of the fraction had a at 275 m with an a of35.9 in iso-octsne. The pos tion and shape of the curve corresponded tothat to b expected of an alloocimene structure.

The acetone condensation product from this fractio was prepared by thesame procedure employed for com pound (1B). The ultraviolet spectrogramof the aceton condensation product had a a at 279 nm with an of 44.6 inmethanol. ,B-ionone has a similar ultraviolt spectrum. The infraredspectre of this condensatio product was also somewhat similar to thespectra c p-ionone. The product had a mint-like odor.

A glassy distillation residue was obtained which has th followingproperties:

(1) The ultraviolet spectrum of the residue in ether ha distinct A butthere was an inflection point at 227 m with an a of 56 and one at 268 ruwith an a of 18.2.

(2) The infrared spectrum of the residue was typic: of a polymericmaterial in that there was no distint bands between 8 and 14 but therewas a broad cor jugated carbonyl absorption at 5.7

(3) This residue was insoluble in sodium carbonat solution but wassoluble in oxygenated organic solvent A summary of the fractionation andspectral data 0 the distillates showed the following approximate yieltoil products from this reaction:

Pei-oer Low boiling conjugated carbonyl material 5.2,3,3-trimethyl-cyclohexadiene-lcarboxaldehydes 28 lerillylaldehyde 312-methyl-2,4,6-octatriene-o-carboxaldehyde 2 Distillation residue 29Loss, due to low boiling compounds 5 Total An infrared spectrum on thetotal liquid pyrolysa analyzed 38% perillylaldehyde which indicates thatth compound and probably others polymerized somewh on distillation.

From this experiment, the reaction may be summarim as presented in theflow sheet.

Flow sheet 1 3 l/ Myrtenal l pyrolysis CH0 CH0 1 CHO Myrtenal wasrefluxed for one and one-half hours at 225-230 C. An infraredspectrogram on the product showed very little change in most absorptionbands. However, there was a new absorption band at 6.07;; due to a newconjugated carbonyl group and/or a CH =C group. There was also a newbroad absorption band at 11.45;; due to a CH =C group. The productcontained some acids, probably due to air oxidation of the conjugatedcarbonyl groups at the elevated temperature. A much longer period ofrefluxing is necessary for a greater conversion to perillylaldehyde andthe other pyrolysis products. Also, an antioxidant should be added orthe reaction carried out in an inert atmosphere such as nitrogen toprevent the formation of acidic material.

EXAMPLE 7 Several sealed glass capsules, each containing a smallquantity of myrtenal, were heated in an oil bath at 265-272 C.Individual capsules were removed at 3 4, /2, l and 2 hour intervals. Thecapsules were cooled and infrared spectrograms made on the products theycontained. The spectra of the products heated for increasing periods oftime showed a gradual disappearance of the myrtenal and at the same timethe appearance of pcrillylaldehyde. A maximum yield of about 40%perillylaldehyde was attained in one hour. The formation of theperillylaldehyde was shown by the appearance of infrared absorptionbands at the following wave-length 6.03. 8.58, l0.86, [1.23. 12.25,12.95.

EXAMPLE 8 M yrtenal was pyrolyzed in the vapor phase by the sameprocedure described in Example except that in this case the temperaturewas maintained at 350 C. An infrared spectrogram on the product showed a41% yield of perillylaldehyde. about 20% unchanged myrtenal and lesspyronene and alloocimene derivatives than at the higher temperaturerange employed in Example 5.

It will be appreciated that the foregoing examples are intended to beillustrative of the invention and to describe the best modes of carryingout the invention as now known. Obviously, many variations therein canbe carried out without departing from the invention. Thus, where estersare pyrolyzed, any suitable ester can be used, such as the propionate,butyrate, benzoate or laurate. Normally the acetate will be employed,however, unless some other particular ester of the isomerized materialis desired. It is. of course, possible and may be desirable in somecases to form the desired ester of the isomerizate by an esterificationstep subsequent to the pyrolysis.

Where the term pinene structure" is used in the claims, it refers to thecarbon-carbon structure of those compounds in which the unbrokencarbon-carbon structure involving the pinene nucleus is limited to thecarbon-carbon structure of a-pinene.

Having described the invention, what is claimed is:

l. The process which comprises heating a myrtenyl compound of thegeneral formula IhCOR wherein R is a monovalent radical selected fromthe class consisting of hydrogen and a monovalent organic radicalattached through a carbon atom thereof to the oxygen atom shown. at atemperature in the range of 225 C. to 700 C. for a time suificient tocause isomerization thereof to monocyclics and acyclics wherein theolefinic bond retains its allylic position to the exocyclic substituentshown.

2. The process which comprises heating a myrtenyl compound of thegeneral formula IhCOlt l \I/ wherein R is a monovalent radical selectedfrom the class consisting of hydrogen and a monovalent organic radicalattached through a carbon atom thereof to the oxygen atom shown, at atemperature in the range of 225 C. to 700 C. for a time sufficient tocause isomerization thereof to monocyclics and acyclics wherein theolefinic bond retains its allylic position to the exocyclic substituentshown and recovering from the isomerizate a fraction enriched in asubstituted allocimene isomeric with the starting material having theCH,OR substituent at the 6-position.

3. The process which comprises heating a myrtenyl compound of thegeneral formula HrCOR wherein R is a monovalent radical selected fromthe class consisting of hydrogen and a monovalent organic radicalattached through a carbon atom thereof to the oxygen atom shown, at atemperature in the range of 225 C. to 700 C. for a time sutficient tocause isomerization thereof to monocyclics and acyclics wherein theolefinic bond retains its allylic position to the exocyclic substituentshown and recovering from the isomerizate a fraction enriched in asubstituted pyronene isomeric with the starting material wherein thesubstituent is the same as the exocyclic substituent shown.

4. The process which comprises heating a myrtenyl compound of thegeneral formula wherein R is a monovalent radical selected from theclass consisting of hydrogen and a monovalent organic radical attachedthrough a carbon atom thereof to the oxygen atom shown at a temperaturein the range of 225 C. to 700 C. for a time sufiicient to causeisomerization thereof to monocyclics and acyclics wherein the olefinicbond retains its allylic position to the exocyclic substituent shown andrecovering from the isomerizate a fraction enriched in a 7-substituted1,8-p-menthadiene isomeric with the starting material wherein thesubstituent is the same as the exocyclic substituent shown.

5. The process which comprises heating a myrtenyl compound of thegeneral formula HzCOR wherein R is a monovalent radical selected fromthe class consisting of hydrogen and a monovalent organic radicalattached through a carbon atom thereof to the oxygen atom shown at atemperature in the range of 225 C. to 700 C. for a time suflicient tocause isomerization thereof to monocyclics and acyclics wherein theolefinic bond retains its allylic position to the exocyclic substituentshown and recovering from the isomerizate separate fractions enriched in(l) a G-substitutcd alloocintene '11.; isomeric with the startingmaterial wherein the substituent is the same as the exocyclicsubstituent shown, (2) a substituted pyronene isomeric with thestartingmaterial wherein the substituent is the same as the exocyclicsubstituent shown, and (3) a 7-substituted 1,8- p-menthadien'e isomericwith the starting material wherein the substituent is the same as theexocyclic suhstituent shown.

6. The process which comprises heating myrtenol at a temperature in therange of 225; to 700 C. for a time sufficient to cause isomerization ofthe myrtenol to monocyclic and acyclic alcohols wherein the olefinicdouble bond retains its allylic position to the hydroxy group.

7. The process which comprises heating myrtenol at a temperature in therange of 225 to 700 C. for a time sufiicient to cause isomerization ofthe myrtenol to monocyclic and acyclic alcohols and recovering perillylalcohol from the isomerizate.

8. The process which comprises heating myrtenol at a temperature in the.range of 225 to 700 C. for a time sulficient to cause isomerization ofthe myrtenoll to monocyclic and acyclic alcohols and recovering from theisomerizate separate fractions enriched in (l) perillyl alcohol, (2) thepyronene alcohols present in the isomeri zate wherein the olefinicdouble bond retains its allylic position to the hydroxy group, and (3)2-methyl-2,4,6 ctatriene-6-carhinol.

9. The process which comprises heating myrtenyl acetate at a temperaturein the range of 225 C. to 700 C. for a time sufiicient to causeisomerization of the myrtenyl acetate to monocyclics and acyclics, andrecovering from the isomerizate separate fractions enriched in (l)perillyl acetate, (2) the pyronenyl acetates present in the isomeriinwhich it is a radical selected from the class consistin of hydrogen anda monovalent organic radical attache through a'carbon thereof to theoxygen atom shown.

lheierenm crew in the file of this patent UNllTED STATES PATENTS2,428,352 Bain et al. Oct. 7, 19 2,453,110 Bain et a1. Nov. 9, 192,537,638 Kitchen Ian. 9,

OTHER REFERENCES Fischer et aL: Berichte d. d. c. Ges., vol. 68B (1935pp. 1730. i732.

1. THE PROCESS WHICH COMPRISES HEATING A MYRTENYL COMPOUND OF THEGENERAL FORMULA